Conventional tobacco stem processed products are rough to the touch and have a greater gravity than leaf flesh tobacco. When the products are used for smoking articles such as cigarettes, they cause an irregularity in the cigarette and undesirable taste due to improper smoke components produced by burning. In addition, the tobacco stems contain more fibers and lignin compared to a tobacco lamina and therefore using the stems gives a fibrous or stimulative smell to the tobacco products.
Various proposals have been made for expanding tobacco stems in order to improve the properties of the stems. Illustrative of prior art in relation to tobacco expansion are as set forth below:
U.S. Pat. No. 3,957,063 to Wochnowski is directed to a method and apparatus for increasing the volume of moist tobacco, wherein particles of a tobacco stream are first expanded by passing through a high-frequency field wherein the particles are exposed to the action of electromagnetic waves which cause a vaporization of moisture in the capillaries with an attendant increase in volume. Thereafter, the expanded particles are introduced into a drying zone by a vibratory conveyor or by a current of a gaseous coolant. In this patent, an increase in volume of up to 50 percent is achieved. Other U.S. Pat. Nos. 3,409,023 and 3,409,027 also disclose the methods similar to the above U.S. Pat. No. 3,957,063.
U.S. Pat. No. 3,704,716 to Abbot, et al., describes a method for the continuous processing of tobacco to expand the tobacco, wherein shredded tobacco is moistened with water to a point at which its volume is about twice the initial volume, continuously moved to a freeze chamber and then to a freeze drying chamber wherein 90 percent of the moisture is removed. Similar methods are available in U.S. Pat. Nos. 3,785,385; 3,823,722; and 3,982,550.
Another U.S. Pat. No. 3,409,022, to de la Burde, relates to a method for puffing tobacco stems, wherein tobacco stems, containing at least 4% to 23% moisture are subject to a radiant energy source under predetermined conditions. By this method, a number of micropores can be created in tobacco stems.
Still another U.S. Pat. No. 3,524,452, to Moser, et al., discloses a method for increasing the filling capacity of tobacco, which comprises wetting a tobacco stream with a volatile organic compound, such as halogenated hydrocarbons, and rapidly vaporizing the liquid from the tobacco by passing the tobacco stream into contact with a rapidly moving stream of gas heated to a temperature above the boiling point of the organic liquid. In this method, the tobacco is expanded in a short period, less than about 4 seconds. Similar processes are available in U.S. Pat. Nos. 3,541,452 and 3,575,178.
Other prior patents describing water or steam treatment have been suggested for puffing tobacco stems. For example, U.S. Pat. No. 4,211,243 to Ohno proposes a method for expanding tobacco stems wherein expanded tobacco stems are produced by heating under pressure tobacco stems which have been separated from tobacco leaves after moisturization at a predetermined pressure and temperature in the presence of superheated steam for 30 seconds or less, and suddenly bringing the pressure to a lower level to cause expanding. U.S. Pat. No. 3,799,176 to Wochnowski relates to a process for processing tobacco, wherein particles of the tobacco stems having a predetermined moisture content, are subjected to the action of a current of a hot gaseous fluid for three successive steps to control the moisture content. U.S. Pat. No. 4,195,647 to Wochnowski, et al, is directed to a method for increasing the volume of tobacco, wherein shredded tobacco is contacted by an upstream of saturated steam and a shower of hot water droplets, the temperature and moisture content of the tobacco thereby increase to a value at which the tobacco is flexible, and thereafter, it is continuously conveyed to a drying unit. In this unit, the shredded tobacco rises and falls while moving across an upstream containing a mixture of superheated water vapors and hot air, thereupon the dried shreds are cooled to room temperature prior to admission into the magazine of a cigarette maker. An alternative method is described in U.S. Pat. No. 3,734,104 to Buchanan, et al., in which high moisture cut stems (about 24 to 60 percent by weight) are subjected to a hot gas containing at least 30 percent steam, whereby the moisturized stems are heated to about 250.degree. to 750.degree. F. for from about 0.5 to 5 seconds. By this process, the filling capacity of the expanded cut stems is increased from 30 to 60 percent or more. A relevant technique is available in U.S. Pat. No. 4,186,755 to Schmidt, not illustrated.
According to these prior patents, tobacco stems can be moisturized by hot water or steam, and then rapidly dried to increase the filling capacity of tobacco. However, those prior methods require expensive chemicals and special apparatus which cause an increase in the production costs. Especially, in the case of microwave or high-frequency energy treatment, uneven properties and blown spots are likely developed on the tobacco. When treating at a high temperature, the tobacco loses its fragrance and a large amount of waste tobacco is produced.